Field of the Invention
The present invention relates generally to an electromechanical system for continuously infusing medication into a patient, and more particularly to a new and improved piston design for a disposable cassette containing a fluid pump therein, which improved piston design utilizes an elastomeric piston cap with an integral boot seal to keep out contaminants, the piston cap being installed over a piston driven by a main pump unit containing a prime mover and a control system for controlling the operation of the fluid pump.
In the past there have been two primary techniques which have been used to deliver drugs which may not be orally ingested to a patient. The first such technique is through an injection, or shot, using a syringe and needle which delivers a large dosage at relatively infrequent intervals to the patient. This technique is not always satisfactory, particularly when the drug being administered is potentially lethal, has negative side effects when delivered in a large dosage, or must be delivered more or less continuously to achieve the desired therapeutic effect. This problem results in smaller injections being given at more frequent intervals, a compromise approach not yielding satisfactory results.
Alternatively, the second technique involves administering a continuous flow of medication to the patient, typically through an IV bottle. Medication may also be delivered through an IV system with an injection being made into a complex maze of IV tubes, hoses, and other paraphernalia. With drop counters being used to meter the amount of bulk fluid delivered, many medications still end up being administered in a large dosage through an injection into the IV lines, although the medications may be diluted somewhat by the bulk fluid.
As an alternative to these two techniques of administering medication to a patient, the relatively recent addition of medication infusion pumps has come as a welcome improvement. Medication infusion pumps are utilized to administer drugs to a patient in small, metered doses at frequent intervals or, alternatively, in the case of some devices, at a low but essentially continuous rate. Infusion pump therapy may be electronically controlled to deliver precise, metered doses at exactly determined intervals, thereby providing a beneficial gradual infusion of medication to the patient. In this manner, the infusion pump is able to mimic the natural process whereby chemical balances are maintained more precisely by operating on a continuous time basis.
One of the requirements of a medication infusion system is dictated by the important design consideration of disposability. Since the portion of the device through which medication is pumped must be sterile, in most applications of modern medication infusion equipment some portions of the equipment are used only once and then disposed of, typically at regular intervals such as once daily. It is therefore desirable that the fluid pump portion of the infusion pump device be disposable, with the fluid pump being designed as an attachable cassette which is of inexpensive design, and which is easily installable onto the main pump unit.
It will be perceived that it is desirable to have a simple disposable cassette design to minimize the cost of construction of the cassette, using the minimum number of parts necessary in the design of the cassette. The design of the cassette must be mass producible, and yet result in a uniform cassette which is capable of delivering liquid medication or other therapeutic fluids with a high degree of accuracy. The cassette should include therein more than just a fluid pump; other features which have formerly been included in peripheral devices may be included in the cassette.
Such a disposable cassette should use a piston-type pump, since piston pumps offer a number of advantages over diaphragm pumps, including better pumping accuracy. It is therefore the primary objective of the present invention to provide an improved piston for use with a disposable cassette. The improved piston design of the present invention will be of a design retaining all of the advantages of such devices known in the past, and will also provide a number of additional advantages and improvements. Specifically, the piston of the present invention shall provide a pump affording a high degree of precision and accuracy, with the degree of precision remaining constant throughout the life of the cassette.
The piston shall also include an integral boot seal both to keep out contaminants, and to ensure that fluid being pumped will not leak out. In order to minimize the number of parts contained in the disposable cassette, it is highly desirable that the piston and the boot seal be manufactured as a single, integral component. In addition, the design of the piston and the boot seal must facilitate quick and convenient sterilization of the entire cassette prior to packaging. No pump design known in the art even comes close to having these features, or even a majority of the features enumerated above.
Despite the inclusion of more features than contained in any competing design, the piston of the present invention shall utilize a minimum number of parts, all of the parts being of inexpensive construction yet affording the assembled cassette the high degree of accuracy which must be retained. The piston, boot seal, and cassette of the present invention must also be of a design which enables it to compete economically with known competing systems. It must provide an ease of use rivaling the best of such competing systems. All these objects must be accomplished in a manner which will retain all of the advantages of reliability, durability, and safety of operation. The design of the present invention must also provide all of these advantages and overcome the limitations of the background art without incurring any relative disadvantage. All the advantages of the present invention will result in a superior medication infusion system having a number of advantages making the system a highly desirable alternative to systems presently available.